The invention relates to an improvement in a linear potentiometer.
In such linear potentiometers, it is known to support a resistance path in a stationary manner in the interior of a housing, which by way of example is tubular, and to cause a wiper contact to slide over this resistance path. Thus the wiper is simultaneously in continuous contact with a parallel pickup path, so that the potential picked up from the resistance path can be transmitted to the outside via the pickup path. The wiper is secured to a push rod which is supported in a longitudinally displaceable manner in the housing. A main bearing is provided at the point where the push rod enters the housing. Conventionally, such bearings are embodied as slide bearings, for instance with the aid of plastic sleeves or the like; but in that case a substantial disadvantage may arise. These bearings will shift out of their proper position comparatively quickly, since it is very difficult if not impossible for the user of the potentiometer to grasp the push rod exactly on the axial center and thereby to avoid any sort of shifting, whether parallel or at an angle. If the push rod is grasped off-center or at an angle, however, a tilting of the main bearing at its entry into the housing necessarily follows, causing the deflection or even the destruction of this bearing.
In linear potentiometers of this kind, whether they are relatively long or short (lengths of a meter or more are not infrequent), it is also possible that the push rod may bend of its own weight, either inside the housing if it is pushed all the way in or outside the housing, so that again the push rod is not in an exactly axially parallel position with respect to its main bearing. Such tilting or shifting is not only disadvantageous in the sense that the bearing may be destroyed, it can also exert negative influences on the functioning of the potentiometer. For instance, if a relatively long, round rod is inserted obliquely into a sleeve-like bearing, the result is a phenomenon which is readily recognizable from general experience and which expresses itself in the form of a shuddering or jerking motion as the rod is inserted or retracted. The reason for this is that the housing of the potentiometer practically assures a linear guidance for the push rod, and if the push rod is tilted as it is introduced it tends to jam in the main bearing because of this tilting. A relatively large amount of force must then be brought to bear in order to move the push rod an additional distance, whereupon it jams again, and so forth.